FIELD OF THE INVENTION
The present invention concerns a process and apparatuses for producing a metal sheet with a corrugation configuration that is of a first predetermined corrugation height, wherein the sheet, transversely or at an angle to the corrugation, has a microstructure with a second, substantially smaller corrugation height. Metal sheets of this kind are processed in particular to form honeycomb bodies for catalytic converters as are used in particular in exhaust gas systems of motor vehicles. The invention however is not limited to that use as for example uses in heat exchangers are also possible.
Details in regard to the form and the advantages of such microstructures are described for example in International
Patent Applications WO 90/08249, corresponding to U.S. Pat. No. 5,157,010, or WO 96/09892. As is already the case in the state of the art, a microstructure in a corrugated sheet denotes a structure which is of substantially smaller height than the corrugation configuration of the sheet. In particular a microstructure can project from a sheet at one or both sides, more specifically for example by at least 15 .mu. or 0.01 to about 0.3 times the corrugation height of the metal sheet.
Corrugated metal sheets are generally produced in the state of the art by corrugation rollers which mesh with each other and which preferably have an involute tooth configuration or a tooth configuration of a similar configuration. Other corrugation shapes, for example a trapezium shape, a zig-zag shape etc. are also known. In a honeycomb body through which exhaust gas flows, in particular in a catalytic converter, microstructures which extend transversely or angled relative to the flow direction, so-called transverse structures (referred to as the TS-configuration), provide for a better transfer of heat between the exhaust gas and the honeycomb body and an improvement in the diffusion procedures which are important in regard to the catalytic effectiveness of the honeycomb body.
The state of the art therefore provides for disposing microstructures at given spacings in succession in the flow direction, in particular at spacings of less than 20 mm and in particular less than 10 mm.
As the microstructures are relatively small in comparison with the typical thickness of the sheets for the honeycomb bodies, it was hitherto assumed that they do not cause problems to a substantial degree in the further manufacturing procedure so that processing was effected using the usual corrugation rollers and moreover with known production steps for forming the honeycomb body.
It has been found however that, when corrugating a sheet that already has microstructures, those microstructures are in part pressed flat again, while in addition that also occurs irregularly, depending on the clearance of the corrugation rollers relative to each other. In that kind of production procedure the microstructures firstly had to be produced with a larger corrugation height than was wanted in the final result, in order to compensate for that effect. When dealing with quite a number of starting materials the cold shaping effects that occur in that situation could only be achieved with difficulty, without causing damage. That problem becomes more acute when dealing with ever thinner sheets and ever smaller corrugation heights. Honeycomb bodies with for example 500 cells per square inch (cpsi) and more are in demand, in which case sheets having a thickness of below 30 .mu.m are used resulting in more serious difficulties in terms of manufacturing procedures.